Roadway surfaces are made from various combinations of aggregate particles and binders. Light duty roadway surfaces, typically made of dirt, gravel and/or stone, are useful for rural roads, farm lanes, private driveways and other situations but often lack binders. For such roadways, the expected volume of traffic is relatively low and it is unreasonable to invest in a black top or concrete roadway surface, which would be quite substantially more expensive. However, conventional light duty roadway surfaces have a number of problems. It would be advantageous if an inexpensive surfacing technique could provide some of the advantages of the expensive ones, such as long term durability, resistance to water damage (especially from freeze/thaw cycles), minimal generation of dust, and smoothness.
Vehicles moving over stone, gravel and similar surfaces cause a stone crushing effect from the grinding together of stones and/or stone particles. This produces dust, some of which remains in the roadway surface, and some of which becomes airborne under the influence of wind or passing vehicles. Airborne dust particles reduce visibility and increase the risk of accidents. Airborne dust creates a nuisance by settling on vehicles homes. people. and anything else in the area of the roadway. The dust is also abrasive and wears vehicle paint. Insofar as dust remains in the roadway, erosion from water is a problem.
Light duty surfaces are not particularly smooth. They develop wheel ruts from traffic and water. Rain, ice and traffic cause potholes. Grading and similar periodic maintenance is needed to keep the surface level or properly crowned, and perhaps to introduce an agent to keep down dust. The deterioration of the surface eventually requires reconstruction or resurfacing.
Moreover, such surfaces generate substantial noise. They are permeable to fuels and oils that leak from vehicles, which may result in the contamination of underground aquifers and surface waters. These and other drawbacks of conventional light duty, low cost surfacing techniques must be balanced against the added cost of the more durable surfaces that are used on more heavily travelled roads and highways.
According to the present invention, a low cost roadway is improved by including strips and particles of preferably-recycled asphalt roofing shingles. The accumulation of waste material in the nation's landfills is a major problem in general, and waste roofing materials in particular are a bulky and heavy form of waste. Asphalt roofing shingle waste is generated, for example, in the manufacture of new shingles, with broken and defective shingles, cutouts, trimmings, and tabs being discarded. Used shingles are frequently discarded when reshingling a roof.
The United States presently produces between 70 and 80 million "squares" of roofing shingles each year, each square representing a quantity of shingles sufficient to cover an area of 100 square feet and weighing between 210 and 235 pounds. Over about the last decade, the construction of shingles has changed. Shingles made before 1980 typically contained. by weight, 50 to 55% asphalt, with the remainder comprising felt or paper reinforcing mat, surface granules, filler, and backing materials. Shingles made after 1980 typically contain, by weight, about 20 to 30% asphalt with the remainder fiberglass reinforcing mat. roofing granules, filler, and backing materials.
A significant portion of asphalt roofing shingle waste is from removal of used shingles. New shingles are flexible and somewhat tacky. After years of exposure, the shingles become brittle and weathered, and are unsuitable for their original purpose. An estimated 60% of the roofing shingles produced go into new construction, and about 40% are used to replace old construction. Thus, a volume of old shingles discarded annually is equal to roughly 40% of the annual production of new shingles--about 20 to 32 million squares or about 2,100,000 to 3,360,000 tons of discarded waste material.
Additionally, a significant volume of associated production waste is generated during the manufacture of roofing shingles. The production of standard three-tab shingles generates cut-outs and trimmings, otherwise known as shingle tabs, that amount to nearly 1% of the weight of a shingle. Hence, even ignoring the volume of broken and defective shingles generated, shingle production results annually in approximately 73,500 to 94,000 tons of waste material containing about 14,700 to 28,200 tons of asphalt.
Traditionally, reclaimed roofing shingle wastes and shingle tabs are discarded into landfills. Asphalt roofing shingles and associated production wastes degrade very slowly, particularly when not exposed to weathering. They accumulate in landfills. Alternative means for disposing of roofing shingles and associated production wastes are needed.
Several attempts to recycle roofing shingle wastes are suggested in the U.S. patent literature. U.S. Pat. Nos. 5,221,338 and 5,223,032 (both Gaudio, et al.) teach the construction. repair and maintenance of asphalt-containing products using asphalt refuse, including roofing shingles. The method includes comminuting reclaimed asphalt shingles to a small particle size; combining the comminuted asphalt shingles with comminuted roughage such as crushed concrete, crushed asphalt pavement, sand and/or stone, and fibrous materials. to form a cold mix of particulated asphalt shingles without heating the asphalt into a liquified state; adding a solvent to the mixture, such as a water-based solvent or oil-based solvent that lubricates, softens, reconditions and/or rejuvenates the recycled asphalt product. The resultant product is a cold mix composition used for repairing, maintaining or constructing asphalt-containing particles, particularly roadway pavement. However. this is accomplished substantially by converting the structure of the shingles into a mix of small aggregate particles in a binder of asphalt. The cold mix is conformable to any pothole or other configuration, i.e., it is workable with a shovel.
A similar approach dealing with roofing shingle wastes is disclosed in U.S. Pat. No. 5,236,497 (Grzybowski). This an reference teaches preparing a similar cold patch composition for pavement repair including the steps of: mixing together recycled asphalt roofing shingles, as a source of asphalt, filler and fiber, with aggregate such as crushed stone, and solvent such as petroleum distillates, without heating, to form a cold patch pavement repair composition that can be worked to conform to the shape of a pothole or the like.
Other patents focus on heat utilizing processes. U.S. Pat. Nos. 4,325,641 (Bobus, et al.) and 4,706,893 (Brock '893) teach methods of recycling asphalt waste shingle tabs or asphalt waste roofing shingles by heating such materials and incorporating them into liquified asphalt paving compositions. Generally, these U.S. patents involve heating of the roofing shingle wastes to melt the asphalt therein and mixing therewith, a certain amount of virgin asphalt and crushed stone or aggregate to form a suitable roadway construction composition.
Still another patent teaches an improvement on the method disclosed in Brock '893. U.S. Pat. No. 5,201,472 (Brock '472) treats asphalt roofing shingles to form a recyclable asphalt material which can be stored, transported, and later used as a component of an asphalt paving composition. Brock '893 teaches that comminuted shingle material must be used quickly after being shredded because the shredded shingle material adheres together after a period of time. After long periods, adverse effects occur on the flowability of the shredded shingle materials and on metering the materials into a recycled mix. Thus. Brock '472 is more particularly directed to a method of storing recyclable shingle materials for extended periods of time without adverse effects on flowability. Particularly, Brock '472 teaches the combining of shredded shingle material with aggregate at a temperature below the melting point temperature of asphalt. According to Brock '472, the resultant mixture of comminuted shingles and aggregate may then be stored prior to recycling into an asphalt-aggregate paving composition without significant agglomeration.
The foregoing attempts to recycle asphalt shingles have in common the aspect that the resulting product is formless, being liquid, or consisting of flowable particles. According to the present invention, a useful product for paving is produced by taking advantage of the form of the recycled materials rather than turning them into a formless moldable composition.
An economical light duty roadway surface, especially for private driveways, farm lanes, and rural roads or other light traffic surfaces, that is simple and cost effective to construct, durable, and reduces the inherent problems of dust and noise associated with conventional dirt. stone and gravel roads. This is accomplished according to the invention by dividing shingle material into strips and using a plurality of the strips to form a layer of roadway wherein the strips overlie one another to provide a form of porous shingle material mat or sheet.